全文获取类型
收费全文 | 9099篇 |
免费 | 654篇 |
国内免费 | 581篇 |
出版年
2024年 | 22篇 |
2023年 | 127篇 |
2022年 | 163篇 |
2021年 | 299篇 |
2020年 | 295篇 |
2019年 | 324篇 |
2018年 | 278篇 |
2017年 | 252篇 |
2016年 | 313篇 |
2015年 | 316篇 |
2014年 | 339篇 |
2013年 | 517篇 |
2012年 | 315篇 |
2011年 | 353篇 |
2010年 | 300篇 |
2009年 | 434篇 |
2008年 | 455篇 |
2007年 | 515篇 |
2006年 | 426篇 |
2005年 | 408篇 |
2004年 | 348篇 |
2003年 | 319篇 |
2002年 | 304篇 |
2001年 | 221篇 |
2000年 | 231篇 |
1999年 | 205篇 |
1998年 | 221篇 |
1997年 | 202篇 |
1996年 | 203篇 |
1995年 | 170篇 |
1994年 | 171篇 |
1993年 | 142篇 |
1992年 | 142篇 |
1991年 | 150篇 |
1990年 | 102篇 |
1989年 | 126篇 |
1988年 | 78篇 |
1987年 | 75篇 |
1986年 | 80篇 |
1985年 | 83篇 |
1984年 | 61篇 |
1983年 | 52篇 |
1982年 | 57篇 |
1981年 | 35篇 |
1980年 | 38篇 |
1979年 | 24篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 9篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
It has been suggested that the sociospatial organization of baboon progressions has a protective function in which the most
physically powerful troop members, the adult males, play a key role. This theory implies regularities in adult male progression
order for different species of savannah baboons with similar social systems. Quantitative progression data are available from
two such similar baboon species, olive and yellow, but not from the third, chacma. The order of movement of 15 adult male
chacma baboons was determined from 40 progressions observed at the Moremi Wildlife Reserve, Botswana. The chacma males were
most often found in the front sixth of progressions, next most often in the second sixth, and about equally often from there
to the rear. As expected from the protection theory, this frontal positioning is consistent with available quantitative data
from other species of savannah baboons. 相似文献
102.
60-Hz electric fields: detection by female rats 总被引:1,自引:0,他引:1
Female rats were trained to detect a vertical, 60-Hz electric field using the same apparatus and procedure we used previously to study behavioral detection of the field by male rats. Each rat was trained individually to press a lever in the presence of the field and not to press in its absence. Correct detections occasionally produced a food pellet. The probability of detecting the field increased as field strength increased. The threshold of detection--ie, the field strength required for detections at a probability of 0.5 after correction for errors--varied among rats between 3 and 10 kV/m. Behavioral detection by female rats was indistinguishable from that by male rats. 相似文献
103.
Dr. G. C. Panzica G. Malacarne A. De Bernochi C. Viglietti-Panzica 《Cell and tissue research》1985,240(1):169-174
Summary Testosterone and corticosterone, administered in doses of 0.5 mg/day for two weeks to three-day-old male chickens, induced alterations in the distributional pattern and in the number of synapses in the rostral neuropil of the hypothalamic paraventricular nucleus. This avian nucleus is a target area for both above-mentioned hormones and also one of the most important centers involved in the regulation of behavioral patterns related to reproduction. Testosterone increased the number of synapses in the rostral paraventricular nucleus, while corticosterone altered their distributional pattern causing an increase in type-B terminals; according to morphological criteria the latter are regarded to represent aminergic endings. Similar results were induced by simultaneous administration of both testosterone and corticosterone. Precocious sexual behavior was also provoked by double treatment.Preliminary results have been presented on the occasion of the 5th ENA meeting (Liège, Belgique, Sept. 1981) and the 1st Italian Meeting of Cell Biology (Rimini, Italy, April 1982)This study was supported by CNR bilateral grants (82.00215.04 & 83.00492.04), MPI 40% and European Training Program in Brain and Behaviour Researchs (twinning grant) 相似文献
104.
Management of a harem breeding colony of rhesus monkeys to reduce trauma-related morbidity and mortality 总被引:1,自引:0,他引:1
M J Kessler W T London R G Rawlins J Gonzalez H S Martinez J Sanchez 《Journal of medical primatology》1985,14(2):91-98
A management procedure was developed for a harem breeding colony of rhesus monkeys to reduce trauma-related injuries and deaths resulting from the periodic removal of pregnant monkeys for research and their subsequent return to the population. Lower morbidity and mortality rates, a reduced mean conception interval, and a higher mean conception rate occurred when monkeys were maintained in permanent harems to which returning females were reintroduced compared to new social groups formed from aggregates of unfamiliar animals. 相似文献
105.
Haruki Ochi 《Environmental Biology of Fishes》1985,12(2):155-160
Synopsis Reproductive behavior of the temperate damselfish, Chromis notata, was investigated on the island of Mukaishima, Japan, almost daily during the breeding season in 1982. Both males and females
repeated reproductive cycles many times during the breeding season. Females had a strong tendency to spawn a whole clutch
on one nest during a few hours. The average number of eggs which a male gained per reproductive cycle was estimated at 38560
(480–131100 eggs). Males ordinarily cared for eggs until just prior to hatching, but abandoned more than half of the nests
with the eggs numbering less than 11568.
Contribution 207 from the Mukaishima Marine Biological Station. 相似文献
106.
Somatic hybridization of Lycopersicon peruvianum and Petunia hybrida was carried out to transfer cytoplasmic male sterility from Petunia to Lycopersicon. Cytological, morphological and biochemical analyses were performed to characterize the regenerated plants. Two regenerated plants, R3 and R6, were male sterile. R3 possessed chromosomes morphologically similar to those of both parental types. Leaf morphologies of these two plants and a third plant, R7, were intermediate between the two parents. The stability of RUBPCase was verified during parental plant development and after in vitro culture. Plant R7 presented a new form of the large subunit of RUBPCase. 相似文献
107.
Robert H. Reed 《The Journal of membrane biology》1984,82(1):83-88
Summary In osmotic experiments involving cells of the euryhaline unicellular green algaChlorella emersonii exposed to hyperosmotic stress by immersion in a range of low molecular weight organic and inorganic solutes, a temporary breakdown in the selective permeability of the plasma membrane was observed during the initial phase of transfer to media of high osmotic strength (up to 2000 mosmol kg–1). Thus, although the cells appeared to obey the Boyle-van't Hoff relationship in all cases, showing approximately linear changes in volume (at high salinity) as a function of the reciprocal of the external osmotic pressure, the extent of change was least for the triitols, propylene glycol and glycerol, intermediate for glucose, sorbitol, NaCl and KCl, with greatest changes in media containing the disaccharides sucrose and maltose. In NaCl-treated cells, uptake of external solute and loss of internal ions was observed in response to hyperosmotic treatment while sucrose-treated cells showed no significant uptake of external solute, although loss of intracellular K+ was observed. These observations suggest that the widely used technique of estimating cellular turgor, and osmotic/nonosmotic volume by means of the changes in volume that occur upon transfer to media containing increasing amounts of either a low molecular weight organic solute or an inorganic salt may be subject to error. The assumption that all algal cells behave as ideal osmometers, with outer membranes that are permeable to water but not to solutes, during the course of such experiments is therefore incorrect, and the data need to be adjusted to take account of hyperosmotically induced external solute penetration and/or loss of intracellular osmotica before meaningful estimates of cell turgor and osmotic volume can be obtained. 相似文献
108.
宁夏枸杞的大、小孢子发生和雌、雄配子体发育 总被引:1,自引:0,他引:1
在幼小花药横切面上,每个角隅处可见一层拱形孢原细胞,其经过平周分裂形成初生造孢细胞、次生造孢细胞,发育为小孢子母细胞。减数分裂过程中胞质分裂为同时型。四分体为四面体型。成熟花粉粒含二细胞,具三孔沟型萌发孔。花药绒毡层由二部分组成:药壁区的绒毡层由初生壁细胞所产生,药隔区的由药隔细胞直接转化成,为双重起源,呈二型性,属分泌型。雌蕊由二个心皮构成二室子房,中轴胎座。倒生胚珠具单珠被、薄珠心,珠被绒毡层。胚囊发育为蓼型。在胚囊细胞分化后,组成胚囊的四种细胞继续发育,表现出各自的形态学变化。 相似文献
109.
Daniel Q. Estep Thomas P. Gordon Mark E. Wilson Margaret L. Walker 《International journal of primatology》1986,7(5):507-517
Copulatory data derived from observations of social groups of rhesus and stumptail macaques were analyzed to test the hypothesis
that pairs of animals would resume copulation significantly sooner if a second male copulated with the female shortly after
the first male’s ejaculation. Data from both groups supported the hypothesis. These results, extending previous studies in Macaca nemestrina,suggest that the shortening of copulatory intervals by social stimuli occurs in several species, both in social groups and
in experimentally created triads. These findings also are consistent with the hypothesis that socially mediated resumption
of mating is related to intrasexual competition among males. 相似文献
110.
Chris L. Schürmann Jan A. R. A. M. van Hooff 《International journal of primatology》1986,7(3):265-287
Recent field data indicate that MacKinnon’s model of the orang-utan’s sexual and agonistic activity needs to be revised. In
this model, male reproductive activity is concentrated in an extended phase of subadulthood and in early adulthood. According
to this model, the role of older adult males is primarily that of range guardian, and in that role they would ensure that
the offspring they had generated earlier would have safe access to food resources. This study presents cases suggesting that
subadult males, even though sexually active, may have low reproductive success. In previous studies adult males were shown
to display less sexual initiative than subadult males. In this study an adult male was at times involved infrequent mating
activity in response to proceptive activity of females in the course of consortship. This adult male proved to be a successful
breeder, thus refuting the hypothesis of adult male sterility. The female is most likely to conceive through cooperative mating
in lengthy consortships with the dominant resident adult male. We hypothesize that the extended subadult phase represents
a submissive strategy, allowing subadult males to remain in the home range of adult males but with minimal reproductive success. 相似文献